REVIEW-2016: change used interfaces and method signatures around Reporting in Jacoco and BuildDashboardReports.

- mark newly introduced interfaces as incubating.
REVIEW-2017: also apply java plugin to check well behavior of jacoco plugin in combination with java plugin.
REVIEW-2024: Make jacoco reporting tests more robust by calculating expected path by reusing constants.
REVIEW-2020: tweaks to template generation in buildSetup task

- always use a template
- use DocumentationRegistry for generating userguide links
- fix wrong referenced apilink
- remove unused property in GenerateBuildFile task